The present invention generally relates to methods and systems for managing air traffic. More particularly, this invention relates to methods and systems used to optimize air traffic control operations and minimize losses in air traffic efficiency, and includes methods and systems for managing the time schedule for arriving aircraft by including early cruise descents as a means of absorbing time delays resulting from one or more aircraft missing its/their scheduled time of arrival (STA).
Managing the time schedule for aircraft approaching their arrival airport is an important air traffic management task performed by air traffic control. It is important to deliver an arriving aircraft to an arrival meter fix within an allowance parameter around a STA, despite interference from weather effects and other air traffic. In modern air traffic, a single airplane missing its STA will have downstream air traffic consequences, possibly including missing landing slots.
An accurate four dimensional trajectory (4DT) in space (latitude, longitude, altitude) and time enables air traffic control to evaluate air traffic and the future location of an aircraft. These parameters can also be used by air traffic control for schedule management purposes to absorb an air traffic delay and change the arrival time of downstream air traffic by longitudinal (speed changes), lateral (flight path lengthening or shortening), or vertical (lowering the cruise altitude to reduce speed) alterations. Currently, a combination of speed changes and lateral alterations in flight paths is used to absorb time delays.
As used herein, trajectory is a time-ordered sequence of three-dimensional positions an aircraft follows from take-off to landing, and can be described mathematically. In contrast, a flight plan is a series of documents that are filed by pilots or a flight dispatcher with a civil aviation authority that includes such information, such as departure and arrival locations and times, that can be used by air traffic control (ATC) to provide tracking and routing services. Trajectory is a means of fulfilling an intended flight plan, with uncertainties in time and position.
Trajectory Based Operations (TBO) is an important component of advanced air traffic systems to be implemented sometime in the near future, including the US Next Generation Air Transport System (NextGen) and the European Single European Sky ATM Research (SESAR). TBO concepts provide the basis for improved airspace operation efficiency. Trajectory synchronization and negotiation implemented in TBO also enable airspace users (including flight operators, flight dispatchers, flight deck personnel, Unmanned Aerial Systems, and military users) to regularly fly trajectories closer to their preferred trajectories, enabling business objectives, including fuel and time efficiency, wind-optimal routing, and weather-related trajectory changes, to be incorporated into TBO concepts. As a result, significant research has gone into developing the system framework and technologies to enable TBO.
An overarching goal of TBO is to reduce uncertainty associated with the prediction of an aircraft's future location through the use of the aforementioned 4DT in space and time. The precise use of 4DT dramatically reduces uncertainty in determining an aircraft's current and future position and trajectory relative to time, and includes the ability to predict when an aircraft will reach an arrival meter fix (a geographic location also referred to as a metering fix, arrival fix, or cornerpost) as the aircraft approaches its arrival airport. Currently, air traffic control relies on “clearance-based control” systems, which depends on observations of an aircraft's current location, typically without much further knowledge of the aircraft's trajectory. Typically, this results in the aircraft flying a route that is determined by air traffic control and which is not the aircraft's preferred trajectory. Switching to TBO would allow an aircraft to fly along a user-preferred trajectory.
In TBO, user preferences determine the choices made in air traffic operations. More specifically, aircraft trajectories and operational procedures are a direct result of the business objectives of the aircraft operator. A fundamental element of these business objectives is the Cost Index, (CI) which is the ratio of time costs (costs per minute) to fuel costs (cost per kg) of an aircraft in flight. The CI of an aircraft determines its optimal flight speed and trajectory, and is a function of atmospheric conditions, aircraft performance capabilities and trajectory, and as a result is nearly unique to every flight. In addition, factors such as speed and altitude do not necessarily increase linearly with increasing CI. As such, the computation of CI in ground simulation is difficult.
Currently, air traffic controllers maintain traffic patterns with the first concern being safety and separation between aircrafts. Such patterns are made with no concern for preferred aircraft trajectories, and as such no efforts are made by air traffic controllers to conserve costs for the aircraft operators. It has been observed that in instances such as this, other viable trajectory changes may be made which are much more cost effective. The optimization and computation required to determine a preferable trajectory would most likely not be possible by a human operator or traffic controller, and would need to be provided by a computer system. In such a case, a computer would provide preferable trajectory options to a human operator, who would then choose from a series of possible trajectories.
For TBO to function effectively, it requires accumulation and compilation of trajectory data from all relevant aircraft. User-preferred trajectories, those which are most desirable by the aircraft operators, may often conflict with one another, especially in air traffic systems which are no longer-clearance based. Although TBO will improve efficiency, it must deal with trajectory and traffic conflicts. Trajectory negotiation determines the trajectory requirements or intentions of a variety of aircraft, and attempts to form a solution which meets as many user preferences as possible and make the best use of available airspace. Such a trajectory negotiation relies on aircraft trajectory data as well as human decision-making and trajectory preferences.
Currently, lateral changes to a flight path, as well as speed changes, are used to absorb air traffic flight delays. However, it would be desirable if early-descent trajectory changes could be used to absorb flight delays in air traffic. The National Aeronautics and Space Administration's (NASA) Ames Research Center has researched the feasibility of using altitude change (descent) advisory capability in NASA's En-Route Descent Advisor (EDA) by conducting human-in-the-loop simulation experiments with experienced Air Route Traffic Control Center (ARTCC) sector controllers, as reported in a paper published at the AIAA Guidance, Navigation, and Control Conference, entitled “Impacts on Intermediate Cruise-Altitude Advisory for Conflict-Free Continuous-Descent Arrival,” Aug. 8-11, 2011, Portland, Oreg. USA.
In a continuous-descent or early-descent trajectory, an aircraft begins descending at an idle or near-idle thrust setting much earlier than in a standard trajectory. By beginning a slow descent much earlier in a flight path, a time delay may be absorbed, and less fuel may be exhausted. The basic outline of an early-descent trajectory is shown in FIG. 1. An aircraft following an early-descent trajectory may either continuously descend to an appointed meter-fix location, or descend to an intermediate lower altitude, allowing it to fly at a slower speed to absorb a flight delay and potentially consume less fuel.
When a time delay in air traffic must be absorbed, early-descent maneuvers may provide a distinct cost advantage over lateral or speed changes to an aircraft's trajectory. However, determining preferable trajectories that meet air traffic safety constraints, absorb proper delay and conserve fuel is most likely beyond the computational capabilities of human controllers, especially if the human controllers are preoccupied with preventing air traffic conflicts. Therefore, a system must be in place which is capable of determining a preferable trajectory, or several preferable trajectories, which may include an early-descent maneuver, and then capable of providing these trajectories to a human controller who can relay the command on to the aircraft pilots. In the event that an air traffic conflict necessitates an aircraft maneuver to absorb a time delay, this system would provide trajectory options preferable to a simple lateral or longitudinal change in aircraft trajectory, while still being conscious of the air traffic safety and operational constraints due to surrounding traffic.
U.S. Patent Application Publication No. 2009/0157288 attempts to solve a similar problem, but limits the actors in the solution to individual aircraft. An aircraft receives only a time delay factor from air traffic control and, in isolation from any additional information from ground systems, determines the best trajectory modification to meet this time delay.
While information and decision-making can be left entirely to either an aircraft or ground systems, there are limitations to the accuracy and availability of information in either of these approaches. Typically, such calculations are contingent on the entirety of air traffic conditions in the vicinity of the aircraft, and therefore the results of such decision making are not isolated to the aircraft.